Recently copper electrochemical deposition processes have become available to form electrically conductive pathways on semiconductor chips. Copper electrochemical deposition process for the damascene structures of high aspect ratios for semiconductor manufacturing is a new application of the conventional electroplating process. The electroplating of high aspect ratio devices involves the use of copper plating to fill high aspect ratio sub-micron trenches and vias positioned on semiconductor chips. An acidic copper sulfate solution of optimized composition has proven to be the best formula for plating micro-features. Typically, the process consists of circulating a plating solution from a reservoir to a plating cell and back to the reservoir. A copper anode in the plating cell provides the source of copper, which is deposited on the cathode comprising a silicon wafer with the damascene structure.
The final performance of the plated wafer depends on the electrical and morphological properties of the deposited copper film. The electrochemical bath composition plays a significant role in deposited copper film properties. The solution concentration of copper and sulfate ions, chloride ions, metallic impurities, and organic additives all are important parameters for providing acceptable copper deposition.
The organic additives added to the bath include accelerators, brighteners, suppressors, and levelers. The combination of these additives determines fling properties as well as the film's initial grain size, brightness or roughness. The optimum bath composition is maintained by periodic analysis and replenishing of the plating bath.
During operation of the bath, the solution is constantly exposed to environmental oxygen as the surrounding air is entrained into the recirculating plating solution. It has been determined that some of the organic additives are sensitive to oxidative decomposition. Accelerated organic additive consumption changes the chemical composition of the bath which, in turn, can adversely affect the acceptability of the deposited copper film. The bath chemical composition can be changed both by the depletion of one or more organic additives and by the increased concentration of organic decomposition produced.
The presence of dissolved gas such as oxygen in the plating bath also can cause the formation of undesirable microvoids in the plated copper film This, in turn, can cause reduced electrical conductivity in the copper pathways formed in the semiconductor surface.
Accordingly, it would be desirable to provide a copper electrochemical deposition process wherein decomposition of organic additives in a copper plating bath is controlled and minimized. In addition, it would be desirable to provide such a process wherein dissolved gas in a copper plating bath is removed.